Updated header.html

Prepended the variable {{ site.baseurl }} to all links, so that the links will use the whole path of the website.

This fixes the bug with the test site not loading files and navigation.
Prepended site.baseurl to about permalink
Prepended site.baseurl to adopt/faqs permalink
Prepended site.baseurl to links in adopt page
Prepended site.baseurl to contact permalink
Updated foster page to prepend site.baseurl in links
Updated greyhounds page to prepend site.baseurl to links
Prepended site.baseurl to flowers permalink
Prepended site.baseurl to volunteer permalink
Updated home page to prepend site.baseurl in links
Merge pull request #28 from gpa-centex/master

Prepended {{ site.baseurl }} to all links